MORBILLIVIRUSES AND MORBILLIVIRUS DISEASES OF MARINE MAMMALS

In recent years, serious disease outbreaks among seals and dolphins we re attributed to infection with established or newly recognized morbil liviruses. The first identification of a morbillivirus as causative ag ent of mass mortality among marine mammals was in 1988, when the previ ously unrecognized phocine distemper virus (PDV) caused the death of 2 0,000 harbor seals (Phoca vitulina) in northwestern Europe. A similar epizootic among Baikal seals (Phoca sibirica) in Siberia in 1987 was l ater attributed to infection with canine distemper virus (CDV). A morb illivirus isolated from stranded harbor porpoises (Phocoena phocoena) between 1988 and 1990 proved to be yet another new member of the genus Morbillivirus, distinct from PDV and CDV and more closely related to rinderpest virus and peste-des-petits-ruminants virus: porpoise morbil livirus. A similar virus, dolphin morbillivirus, was the primary cause of mass mortality among striped dolphins (Stenella coeruleoalba) in t he Mediterranean from 1990 to 1992. In this review, current knowledge of the genetic and antigenic relationships of these viruses is present ed, and the origin and epizootiological aspects of the newly discovere d morbilliviruses are discussed. In addition, the possible contributor y role of environmental contaminant-related immunosuppression in the s everity and extent of the different disease outbreaks is discussed.